This invention relates to a drive for a demolition tool designed as a crushing jaw or shear assembly having two tool blades which together define a variable tool mouth receiving the material to be crushed. The drive includes at least one hydraulic cylinder by means of which at least one of the tool blades can be moved relative to a carrier body on which the tool blades mounted.
Depending on whether the demolition tool is designed as a crushing jaw assembly or a shear assembly, its tool blades are two jaws or shear arms which are movable relative to one another and which act on the material to be crushed.
In current demolition tools the drive is usually constituted by one or more hydraulic cylinders with which both tool blades may be driven simultaneously, as disclosed, for example, in German Patent No. 3,342,305 (to which corresponds U.S. Pat. No. 4,512,524 and which relates to crushing jaws) or European Patent Application 218,899 (relating to crushing shears).
Demolition tools of the above-outlined type are used as assemblies attached to carrier equipment, particularly hydraulic excavators. The available hydraulic output (flow rate and operating pressure of the hydraulic fluid) is predetermined by the hydraulic assembly, acting as the energy source. Stated differently, the hydraulic energy is available for the demolition tool only within a limited range. For reasons of economy, however, the drive should be able to rapidly move the tool blades during the closing and opening process and apply a large working force when acting on the material to be crushed. For the above reasons the drive for demolition tools has to be adapted to the hydraulic power of the energy source and the operating conditions.
The above-outlined problems can in part be overcome by measures disclosed in Japanese publications JP-B 2-59/16,613 and JP-A-62/83,504. According to these references, the hydraulic cylinder has associated internal or external pressure transformer with which the operating pressure delivered by the energy source can be increased to obtain the large operating forces required for the crushing of the material. Such a system, however, requires the use of particularly sturdy components, seals, hoses and screw connections.
German Offenlegungsschrift (application published without examination) 33 46 235 proposes to increase the operating speed of a hydraulic cylinder by means of a control unit such that a fluid equalization is effected between the two piston surfaces. Although by returning the fluid, displaced by the piston, into its operating pressure chamber, the quantity of hydraulic fluid to be supplied by the energy source of the carrier equipment can be reduced, the magnitude of the operating force and the speed of the working movement of the hydraulic cylinder are predetermined by the cross section of the piston rod.